With so much emphasis being placed on fuel economy, engine performance and exhaust emissions, a majority of today's vehicles powered by an internal combustion engine include electronic engine control systems with strategies for controlling various features of the engine's operation including the air/fuel ratio (i.e., ratio of the mixture of charging air and fuel supplied to the engine) and/or various engine exhaust system temperatures.
The air/fuel ratio is controlled to optimize fuel economy and engine performance. It may also be used to control various temperatures associated with the exhaust system, in particular the temperature of the engine exhaust gases. Certain temperatures associated with the exhaust system are controlled apart from the air/fuel ratio.
Thus, most internal combustion engine vehicles include an exhaust system with an exhaust manifold connecting the engine with the remainder of the exhaust system, and a catalytic converter and one or more exhaust gas oxygen (EGO) sensors up stream from the catalyst for emissions control purposes. It is important to know and control the temperature at various locations along an engine's exhaust system. For example, the temperature inside the catalytic converter must be controlled to protect against the catalyst being damaged from overheating. It is also important to know the temperature of each EGO sensor because these sensors should typically be warmed up before being operated. Electronic engine control systems which employ EGO sensors often control one or more heaters for warming up the EGO sensors. Thus, the temperature of each EGO sensor should be identified in order to most efficiently and effectively utilize the heaters. Such control systems also often include a closed loop fuel control strategy to optimize exhaust emissions. However, until the EGO sensors are operational, the engine control system is unable to properly utilize its closed loop fuel control strategy.
Therefore, in properly controlling an engine's operation, it is often necessary for the temperature at such locations in the engine's exhaust system, as well as the temperature at other locations considered important in controlling the engine's operation, to be identified at the time the engine is started. By knowing the initial temperature at such locations, the air/fuel ratio, the exhaust system and other features of the engine's operation can be more accurately controlled at the initial stages after the engine is turned on. Rather than incurring the expense associated with being directly measured, some engine control strategies have these initial exhaust system temperatures, and other temperatures, preset in their software. However, these preset temperatures often do not correspond to the actual temperatures with sufficient accuracy. By using an actual soak time for the engine, previously preset temperatures could be more accurately inferred. Soak time is the time between when the engine is turned off and then restarted. Previous electronic engine control systems have included a timer for measuring the actual soak time of the engine. The soak time is then used with existing engine control strategies to infer initial exhaust system, as well as other, temperatures following a soak.
However, not all vehicles are designed with a soak timer in its engine control system, and incorporating a soak timer into such a system is costly. Therefore, there is a need for an inexpensive way to incorporate soak time strategy in an engine control system not originally designed to use actual soak time strategy. In addition, because there is a continuing need to lower costs, there is also a need for a way to eliminate the expense of using an actual timer to obtain soak times for those engine control systems which are already designed to use soak time strategy and hardware.